Exploring high-albedo event craters in the near-polar permanent ice cap of Mars

This study focused on the water-frost/ice and carbon dioxide frost interactions in impact craters of the northern seasonal polar ice cap on Mars. Studying the interaction between water and carbon dioxide frost/ice within the outer permanent ice cap can help us in determining the role of these two materials in the hydrological and geological cycles, as well as the possible biological cycle (if any) on Mars. Using THermal EMission Imaging System (THEMIS) infrared and visible images, Thermal Emission Spectroscopy (TES) Lambert albedo and target temperature data and Mars Orbital Laser Altimeter (MOLA), a detailed study of seven previously identified craters with high albedo events (HAEs) in the period of late spring to late summer was carried out. Results indicate six of the seven observed impact craters with both AM and PM HAEs are associated with a permanent water-ice body (or patch) covering a part or all of those crater floors, while one impact crater with AM-only HAEs is not associated with a permanent water-ice body. This observation is consistent with a conceptual model proposed by Xie et al. [in press] that an exposed permanent water-ice body is the basis for the AM and PM HAEs in those craters, while a subsurface water ice body or ice-rich regolith in the near subsurface is a necessary condition for the AM-only HAEs crater. Variations in albedo in Phases 2 and 3 of the Martian annual cycle are found in some craters. This is mainly due to the exposed, permanent water-ice body (patch) that is only a small portion of the crater floor, resulting in a limited contribution from the water-ice body to the albedo change of the entire crater floor measured from the TES instrument.